US4106018A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Method and apparatus for reducing interference between plural radio altimeters
Assignee: Boeing North American Inc
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Filing: 1977-04-18
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Granted: 1978-08-08
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Expires: 1997-04-18
Abstract
Abstract A method and apparatus for independently controlling a CWFM radio altimeter to reduce interference from another nearby altimeter employs a high-Q filter outside the bandpass of the signals which are developed and decoded for altitude indication to detect an approaching interference signal received from the other altimeter and produce an output to a threshold detector. When the output of the filter exceeds a predetermined level, the threshold detector causes the transmitted frequency of the altimeter to be stepped. In one embodiment, a digital counter is provided to cyclically count up and down at a desired sawtooth modulation frequency. The output of the counter is applied to a digital-to-analog converter to produce an output used to control the frequency of the transmitted signal. Additionally, the output of the counter is conducted to inputs of an adder having a preset add number therein. When the output from the threshold detector is produced, it loads the counter immediately with the sum of the present counter output with the preset add number. The counter then begins its count at the totalled count, thereby immediately stepping the transmitter frequency. In redundant systems, each transmitter frequency can be shifted a different amount in an individual preset direction.
Inventors
- 👤 Paul P. Chihak
- 👤 Charles H. Wehage
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-01 02:41
CPC Classifications
G; G01; G01S; G01S7/00; G01S7/02; G01S7/36; G01S13/00; G01S13/02; G01S13/06; G01S13/08; G01S13/32; G01S13/34; G01S13/345; G01S13/88; G01S13/882
Claims Analysis
Total Claims: 20
Claim 1
Independent Claim
145 words
Apparatus for independently controlling the phase of the modulating frequency of a transmitter of at least one of at least two simultaneously operating CWFM ratio altimeters to reduce interference between said at least two altimeters, comprising: a filter connected to continuously receive a signal generated by said at least one altimeter, said signal having a frequency equal to the difference between a signal transmitted by said at least one altimeter and a signal recieved by said at least one altimeter to indicate altitude; said filter having a bandpass centered about a frequency above and essentially outside of the bandpass of frequencies of said altitude indicating signal to pass frequencies approaching the bandpass of said altitude indicating signal; a threshold detector receiving an output of said filter, and means responsive to an output of said threshold detector to step said at least one altimeter transmitter frequency.
Claim 2
Dependent Claim
145 words
Apparatus for independently controlling the phase of the modulating frequency of a transmitter of at least one of at least two simultaneously operating CWFM ratio altimeters to reduce interference between said at least two altimeters, comprising: a filter connected to continuously receive a signal generated by said at least one altimeter, said signal having a frequency equal to the difference between a signal transmitted by said at least one altimeter and a signal recieved by said at least one altimeter to indicate altitude; said filter having a bandpass centered about a frequency above and essentially outside of the bandpass of frequencies of said altitude indicating signal to pass frequencies approaching the bandpass of said altitude indicating signal; a threshold detector receiving an output of said filter, and means responsive to an output of said threshold detector to step said at least one altimeter transmitter frequency.
Claim 3
Dependent Claim
12 words
The apparatus of claim 1 wherein said filter is a high-Q filter.
Claim 4
Dependent Claim
16 words
The apparatus of claim 1 wherein the bandpass of said filter is centered about 500 kHz.
Claim 5
Dependent Claim
79 words
The apparatus of claim 1 wherein said means responsive to an output of said threshold detector to step the transmitter frequency comprises: a counter connected to cyclically count up and down, means responsive to the up and down count of said counter, to produce a sawtooth modulation waveform of said transmitter frequency in response to said count, and means to change the count of said counter by a preset amount in response to the output of said threshold detector.
Claim 6
Dependent Claim
57 words
A plurality of apparatuses for independently controlling the phases of the modulating frequencies of the transmitters of a plurality of respectively associated simultaneously operating CWFM radio altimeters to reduce interference therebetween, each of said altimeters comprising: means for detecting outside an acceptable signal bandpass the approach in frequency of interference signals toward the acceptable signal bandpass, and
Claim 7
Dependent Claim
57 words
A plurality of apparatuses for independently controlling the phases of the modulating frequencies of the transmitters of a plurality of respectively associated simultaneously operating CWFM radio altimeters to reduce interference therebetween, each of said altimeters comprising: means for detecting outside an acceptable signal bandpass the approach in frequency of interference signals toward the acceptable signal bandpass, and
Claim 8
Dependent Claim
13 words
means for stepping the transmitter frequency when said approach in frequency is detected.
Claim 9
Dependent Claim
13 words
means for stepping the transmitter frequency when said approach in frequency is detected.
Claim 10
Dependent Claim
26 words
The apparatuses of claim 5 wherein each of said stepping means is preset to step its associated altimeter transmitter frequency with a unique direction and magnitude.
Claim 11
Dependent Claim
40 words
The apparatuses of claim 5 wherein each of said detecting means comprises a high-Q filter to which a received signal is applied, and a threshold detector receiving an output from said filter to produce a signal to said stepping means.
Claim 12
Dependent Claim
69 words
The apparatuses of claim 7 each of which further comprising a counter to which said threshold detector output is applied operating to load a preset number into said counter. said counter operating cyclically up and down to produce an up and down count, and a digital-to-analog converter to which said up and down count is applied to produce a sawtooth output in accordance with which said transmitter is modulated.
Claim 13
Dependent Claim
52 words
The apparatuses of claim 8 each of which further comprising an adder to which the output of said counter is applied, signal producing means connected to selected inputs of said adder to define said present number to be added to the output of said counter when said threshold detector produces an output.
Claim 14
Dependent Claim
24 words
The apparatuses of claim 9 each of which further comprising an oscillator connected to clock said counter at a frequency of about 51.2 kHz.
Claim 15
Dependent Claim
16 words
The apparatuses of claim 7 wherein said high-Q filter has a bandpass centered about 500 kHz.
Claim 16
Dependent Claim
14 words
The apparatuses of claim 5 wherein the CWFM ratio altimeters are three in number.
Claim 17
Dependent Claim
20 words
The apparatuses of claim 12 wherein said stepping means are preset to step each transmitter 90°, 45°, and 221/2°, respectively.
Claim 18
Independent Claim
87 words
A method of reducing the interference between redundant simultaneously operating CWFM ratio altimeters of the type which transmit a signal and receive a reflection of the transmitted signal, comprising: detecting a frequency approaching interference signal transmitted by one of said altimeters and received by at least another of said altimeters outside of the bandpass of desired altitude indicating signals of said another of said altimeters, and stepping a transmitter frequency of said at least another of said altimeters in response to detecting a frequency approaching interference signal.
Claim 19
Independent Claim
87 words
A method of reducing the interference between redundant simultaneously operating CWFM ratio altimeters of the type which transmit a signal and receive a reflection of the transmitted signal, comprising: detecting a frequency approaching interference signal transmitted by one of said altimeters and received by at least another of said altimeters outside of the bandpass of desired altitude indicating signals of said another of said altimeters, and stepping a transmitter frequency of said at least another of said altimeters in response to detecting a frequency approaching interference signal.
Claim 20
Dependent Claim
32 words
The method of claim 14 wherein said detecting step comprises: applying a mixed altimeter signal to a high-Q 500 kHz filter, and detecting a threshold level of an output of said filter.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1981-08-07 | 1982-02-06 | 1982-08-08 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1985-08-07 | 1986-02-06 | 1986-08-08 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1989-08-07 | 1990-02-06 | 1990-08-08 | $7700.00 | Window Closed / Lapsed |